Reconditioning catalytic cycle stocks



Feb. 8, 1944. A. A. WELLS 2,341,405

RECONDITIONING CATALYTIC CYCLE STOCKS Filed June 24, 1940 C O/V-DE'ALSER 25c E vI/vc CATALYTIC} HEA TIA/6 j 0 o o HEAT/N6 c014 O O O FEED Patented F- 8,

UNITED STATES PATENT omen Alfred A. Wells, Roselle Park, N. 3., asslgnor to Standard Oil Development Company, a corporatlon of Delaware Application June 24, 1940, Serial N5. 342,031

lclaim.

The present invention relates to the art of treating hydrocarbons. More particularly, the present invention relates to improvements in the catalytic treatment of relatively heavy hydrocarbons such as a gas oil to form fractions boiling within the gasoline range, in which process the cycle stock, that is to say, the unconverted hydrocarbons recovered from the catalyst zone are subjected to a conditioning operation in order to improve their cracking characteristics or properties when recycled to the cracking zone.

It is generally known that in the cracking of hydrocarbons thermally, the charging stock should be largely paraflinic to produce the best results. It is also known that the more a charging stock is cracked thermally, the poorer it becomes as a feed stock for further cracking. Consequently, in thermal operations there comes a time when the feed stock, due to repeated cracking, must be rejected from the systembecause it becomes too refractory and has too great a tendency to form excessive coke to be suitable for further treatment.

0n the other hand, the feed stock for a cata lytic cracking operation is preferably of a naphthenic character and should also be free, or substantially so, of aromatic compounds containing more than one benzene ring in a single con densed nucleus. If a feed stock used in a catalytic cracking operation contains compounds such as naphthalene, anthracene, phenanthrene, benzanthrene and the like, or their alkylated derivatives, these condensed ring compounds form, during the cracking operation, excessive quantities of coke. Furthermore, if a feed stock in a catalytic cracking operation contains substantial quantities of olefins, and especially the diolenns or poly-olefins. these latter compounds during the catalytic cracking operation tend to polymerize to form high molecular weight hydrocarbons which, during the catalytic conversion, are converted to tarry or gummy deposits or coke which deposit on the catalyst and necessitate frequent shutdowns for the purpose of re-'- moving the same and regenerating the catalyst.

I have discovered means for conditioning the cycle stock or recycled oil recovered from a catalytic operation wherein the same is improved as to its cracking properties and therefore may be recycled to the catalyst zone for further conversion without causing excessive formation of tarry deposits or coke on the catalyst.

It is an object of my invention to condition an oil such as a cycle oil recovered from a catalytic process, which all is not satisfactory from the standpoint of cracking characteristics, by subjecting the said oil to a catalytic treatment wherein the tar-forming constituents are converted to high molecular weight compounds which may be removed from the said oil so that the said all may be returned to the cracking zone for further treatment with the assurance that such treatment will not result in the formation of excessive quantities of coke;

A proper understanding of my invention will be had by reference tothe accompanying drawing in which the figure represents in diagrammatic form, an apparatus layout in which my process may be carried into practical effect.

Referring in detail to the drawing, a feed stock such as a virgin gas oil having an A. P. I. gravity of 25? is fed to the system through line I and thence discharged into a coil 2 disposed in a furnace setting 3 where the hydrocarbon oil is heated to cracking temperatures, say a temperature of about 825 F. The hydrocarbon vapors are withdrawn from the furnace through line 4 and discharged into a catalytic cracking chamberi, where the vapors contact a cracking catalyst such asan acid treated clay, and under the conditions specified the gas oil vapors are converted to gasoline in yields amounting to 40%50% of the original feed stock. The total vapors are withdrawn from the reaction vessel 6 through a vapor line H) and then passed into a fractionating column l2 where the vapors are fractionated, the gasoline fraction being withdrawn overhead through line l4, thence discharged into a condenser li where the gasoline vapors are liquefied, thence discharged through line It into a receiving drum l9 from which the gasoline may be recovered through line 20. Meanwhile, heavy oil or a highv boiling fraction is withdrawn through line 2|, while a lighter or lower boiling fraction is withdrawn'through line 22, the latter being thence discharged into coil 23 disposed in a furnace 24 where the unconverted gas oil is heated to a temperature suflicient to vaporize the same, say a temperature of 600-800 F. The oil vapors are withdrawn from the furnace 23 through line 25 and thence discharged into the top of a tower 21 which is preferably packed with kaolin or Florida earth, bauxite and the like, which latter has a catalytic effect, where they .are conditioned by the polymerization of unsaturated bodies contained in the vapors, such unsaturated bodies being olefins, dioleflns, and similar unstable constituents. The temperature of the clay tower should preferably be such as to maintain the oil in a vaporous state, preferably between 350 Rand 750 F. The pressure may be at atmospheric or above. The polymerization products are, for the most part. in a liquid form and are withdrawn from the bottom of tower 21 through pipe 28. Preferably a heavy gas oil is discharged from line 29 intotower 21' for the purpose of washing the clay-to assist in the removal of the heavy fractions and/or polymerization or condensation products from the clay or valved line 32, thence into a fractionating column 3! from whichthe polymerization liquid portion not removed from the vapors through line 28 in tower 21 may be withdrawn from tower 3| through line 3|, and the conditioned gas oil vapors substantially free of polymerization products are withdrawn overhead through line 35 and thence discharged into line 33 for transfer to the inlet side of coil 2. s

While I prefer to treat the hydrocarbon oil in vapor form in reaction chamber 21, it is within.

the purview of my invention to operate in the liquid phase in chamber 21;

Referring back to the cycle stock treated in chamber 21, it is pointed out that the best operating conditions obtained in this chamber depend on the nature of the recycled'oil, that is to say, depending on the boiling range of the recycled oil and on the amount of polymerizable material contained therein, as well as other factors. Generally, it may be said that good results are obtained by operating at a temperature within the range of from 350 F.-750 F., employing either atmospheric or a superatmospheric pressure ofsay from 1-3 atmospheres gauge, or higher, and permitting a suflicient time of contact between the recycled oil and the adsorbent, say from seconds to 3-5 minutes, to permit the desired conversion.

It is pointed out withrespect to the temperature of the vapors entering treating tower I1 that the same should be at least above the dew point,

and preferably should be from '-100',l". above the said dew point.

It is further pointed out that not only polymerization takes place in chamber 21, but also that unstable aromatic compounds which contain two or more aromatic rings ina single condensed nucleus are decomposed and recombined in some manner which is not exactly clear, to form heavy hydrocarbons which are relatively poor in hydrogen content which may be retained in the adsorbent material or subsequently with drawn through lines 2; or 34'. Many modifications of my invention may be made by those skilled in this art without departing from the spirit thereof. v

What I claim is:

A process for the conversion of'hydrocarbon oils which comprises passing the fresh oil to be converted through a cracking zone, contacting said oil within said cracking zone with an active cracking catalyst, maintaining said 011 during passage through said cracking zone at a cracking temperature, keeping said oil incontact with said catalyst within said cracking zone for a period suflicient to convert a substantial portion thereof into motor fuel, thereafter fractionating the cracked products to segregate a condensate ALFRED A. WELLS. 

